There has been reported a planer light source device using an optical semiconductor device (e.g., LED) in which a large number of grooves having a shape of a semi-circular in sectional view are formed concentrically in order to scatter light (e.g. see Reference 1).
[Reference 1] JP 2000-184137 A
However, in the planar light source device described above, sufficient uniformity of light emission in a plane has not been obtained yet.